Projection lamp including a blackening control device



Oct. 17, 1967 R. E. SMITH 3,343,094

PROJECTION LAMP-IiJCLUDING A BLACKENING CONTROL DEVICE Filed Dec. 28, 1965 FIG.I

RICHARD E. SMITH INVENTOR ATTORNEY United. States Patent 3,348,094 PROJECTION LAMP INCLUDING A BLACK- ENING CONTROL DEVICE Richard E. Smith, Lexington, Ky., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Dec. 28, 1965, Ser. No. 516,991 Claims. (Cl. 315-71) ABSTRACT OF THE DISCLOSURE A projection lamp including a blackening control device in the form of a probe connected through a high resistance to one of the voltage contact pins.

This invention relates to electric incandescent lamps and more particularly to lamps designed primarily for use as light sources in photographic projection devices, such as motion picture projectors for example.

Projection lamps are operated at temperatures considerably higher than the operating temperatures of many other incandescent lamp types, such as those used for residential lighting for example. Thus projection lamps have a relatively short life because they have a relatively high rate of filament evaporation. This high rate of filament evaporation also adversely affects lumen maintenance during life because of the discoloration or blackening of the reflector and/or the bulb wall due to the deposition of tungsten thereon.

In view of the foregoing, one of the principal objects .of this invention is to improve the lumen maintenance of projection lamps during life.

This and other objects, advantages and features are attained, in accordance with the principles of this invention, by providing the lamp with a blackening control device. In the specific embodiment of the invention illustrated in the accompanying drawing and described below, the blackening control device is in the form of a probe connected through a high resistance to one of the voltage contact pins. The probe is preferably disposed substantially parallel to the lamp filaments and spaced a few millimeters therefrom.

In the accompanying drawing, FIGURE 1 is a front elevational view of a projection lamp with which the blackening control device of this invention may be employed.

FIGURE 2 is a side elevational view of the lamp of FIG. 1.

FIGURE 3 is a transverse sectional view of the lamp of FIG. 1, taken along the line 33 thereof.

In the specific embodiment of the invention illustrated in the accompanying drawing, the projection lamp comprises a substantially tubular lamp envelope 2, one end of which is constricted to define a bulb neck 4. A glass disc or header 6 is hermetically sealed to the bulb neck 4 and this end of the lamp is provided with base 8 which is secured thereto by basing cement 10. The header 6 is provided with a plurality of spaced nubbins or bosses 12 through which stiff lead-in wires 14, 15, 16 and 17 are sealed. The inner ends of these lead-in wires serve as support members and the other ends thereof project through holes provided therefor in the base 8 and serve as electrical contact members for engagement in a lamp socket or other suitable receptacle. A central post 18 depends from the base 8 and serves the dual purpose of providing a protective enclosure for the lamp exhaust tube tip and, by means of a keyway 19 with which it is provided, aids in the proper orientation of the lamp in its socket or receptacle.

A reflector 20, comprising a glass piece having a coat- ICC.

ing of light-reflecting material thereon, is disposed within the lamp envelope 2 and spaced therefrom. The reflector '20 is provided with a centrally located, elongated aperture within which a ceramic plug 22 is fitted. Filament support wires 24 and 26 extend through the ceramic plug 22 and are secured therein. A main filament 28 is supported by the wires 24 and 26 near the front ends thereof. One end of a ballast filament 30 is secured to the support wire 26 near the front end thereof, and the other end of the ballast filament 30 is secured to one end of a connecting rod 32. The other end of the connecting rod 32 is secured to lead-in wire 14. Wire 34, which functions as a fuse-protected by a glass sleeve 36, connects the rear end of the filament support wire 24 to lead-in Wire 15.

A substantially rectangular spring steel clip 38 having a centrally located elongated aperture is slipped over the ceramic plug 22. The clip 38 has turndown corners a which abut the back of the reflector 20. The reflector 20, plug 22 and clip 38 are accurately and firmly secured to one another by wedges 40 which are driven through the plug 22 from opposite sides thereof and through the a slot provided therefor in the plug. The spring clip 38 is provided with a U-brace 42 secured thereto across the lower end thereof. Struts 44 and 46 are each attached at one end thereof to a leg of the U-brace 40, the other end thereof being attached to lead-in wires 16 and 17 respectively. Thus the struts 44 and 46, through the U-brace 40, support the spring clip 38 from the lead-in wires 16 and 17. Rigidity of the inner ends of the lead-in wires 16 and 17, and thus an assured uniform spacing of these wires from one another, is obtained by the U-brace 48.

Mounted on lead-in wire 16, extending substantially parallel to filaments 28 and 30 and spaced a few millimeters (about 2-4 for example) therefrom is a blackening control device in the form of a probe 50 of 20 mil molybdenum wire. The locus of this probe 50 is also related to the orientation of the lamp in its socket or receptacle so that it is located above the filaments when the lamp is burned horizontally. The probe 50 is connected through a high resistance to one of the voltage contact pins 14. As shown in FIG. 3, the high resistance connection is in the form of a thin line of graphite 52 (diluted with glass powder) painted on the header 6 between the pins 14 and 16. The value of this high resistance should be sutficiently high to prevent excessive corona or areover from the proble 50 to filament 28; yet it should be sufliciently conductive to accomplish its vapor-trapping function. Resistances between 400 and 200,000 ohms have been found to give satisfactory results. This blackening control device has been found to improve lumen maintenance from 160% to at /a life.

Although the exact nature of the probe action is not known precisely, it is believed that the tungsten particles which leave the hot filament are probably charged-for a short time and distance-as they are vaporized from the filament. With the probe 50 disposed as described above and energized to subject these particles to an electric field, direction of the deposition of the particles may be regulated and controlled. A current from the filaments 28 and 30 to probe 50 can be measured. This circuit behaves as though a space charge is present. If the resistance 52 is too low, a high intensity corona burns out the resistance and occasionally triggers an arc across the extreme terminals of the filaments. However, when the resistance 52 is within the limits noted above, the space current is stabilized at a value which does no damage but does prevent excessive deposits of tungsten on the reflector and the bulb wall.

While there has been shown and described what is at present considered the preferred embodiment of the inenvelope; a filament disposed in said envelope and connected to two of said lead-in wires; a reflector disposed in said envelope and spaced from the inner Wall thereof,

said reflector being further disposed in light-reflecting relationship with respect to said filament; means for supporting said reflector disposed as aforesaid; a probe mounted on one of said lead-in wires and extending substantially parallel to and close to said filament; and high resistance means connecting said probe to a voltage source. a r r r 2. The combination of claim 1 in which the hermetically sealed glass envelope includes a header and the high resistance means connecting said probe to a voltage source is a line of graphite painted on said header.

3. The combination of claim 1 in which the voltage source to which said high resistance means is connected is one of said lead-in Wires.

4. The combination of claim 1 in which the said probe References Cited UNITED STATES PATENTS 2,467,710 4/1949 Van Horn 313217 2,494,916 1/1950 Van Horn 31323l X 2,530,990 11/1950 Peters 313.348 X 3,160,776 12/1964 Cardwell 313113 X JAMES W. LAWRENCE, Primary Examiner. R. JUDD, Examiner. 

1. A PROJECTION LAMP COMPRISING: AN HERMETICALLY SEALED GLASS ENVELOPE; A PLURALITY OF LEAD-IN WIRES SEALED IN SAID ENVELOPE; A FILAMENT DISPOSED IN SAID ENVELOPE AND CONNECTEDF TO TWO OF SAID LEAD-IN WINES; A REFLECTOR DISPOSED IN SAID ENVELOPE AND SPACED FROM THE INNER WALL THEREOF, SAID REFLECTOR BEING FURTHER DISPOSED IN LIGHT-REFLECTING RELATIONSHIP WITH RESPECT TO SAID FILAMENT; MEANS FOR SUPPORTING SAID REFLECTOR DISPOSED AS AFORESAID; A PROBE MOUNTED ON ONE OF SAID LEAD-IN WIRES AND EXTENDING SUBSTANTIALLY PARALLEL TO AND CLOSE TO SAID FILAMENT; AND HIGH RESISTANCE MEANS CONNECTING SAID PROBE TO A VOLTAGE SOURCE. 